1. Field of the Invention
The present disclosure relates to a high pressure water electrolysis system and a method for activating the high pressure water electrolysis system.
2. Discussion of the Background
In general, hydrogen is used as a fuel gas used for electricity generating reaction of fuel cells. The hydrogen is produced, for example, by a water electrolysis unit. The water electrolysis unit employs a solid polymer electrolyte membrane (ion-exchange membrane) for decomposing water to generate hydrogen (and oxygen). Electrode catalyst layers are provided on both sides of the solid polymer electrolyte membrane to form an electrolyte membrane electrode assembly, and power feeders are disposed on both sides of the electrolyte membrane electrode assembly to form a unit cell.
A plurality of unit cells are stacked to form a cell unit. A voltage is applied to both ends of the cell unit in the stacking direction, and water is supplied to the anode-side power feeders. On the anode side of each electrolyte membrane electrode assembly, the water is decomposed to generate hydrogen ions (protons). The hydrogen ions move through the solid polymer electrolyte membrane to the cathode side, and combine with electrons to produce hydrogen. On the anode side, oxygen generated together with the hydrogen is discharged together with surplus water from the cell unit.
In order to generate high pressure hydrogen at several tens of MPa in this type of water electrolysis system, for example, a method and apparatus for producing high pressure hydrogen disclosed in Japanese Unexamined Patent Application Publication No. 2007-100204 is known. Japanese Unexamined Patent Application Publication No. 2007-100204 is characterized in that hydrogen obtained at the cathode by electrolysis of pure water using an electrolysis cell is taken out of the reaction system while maintaining the pressure of the hydrogen at a predetermined pressure or higher.
In a water electrolysis system generating high pressure hydrogen, when stopping the water electrolysis system, the high pressure hydrogen line in the water electrolysis unit (electrolysis cell) needs to be returned to the normal pressure (atmospheric pressure). The reason is that if the solid polymer electrolyte membrane is always subjected to the pressure difference, the solid polymer electrolyte membrane is easily damaged.
So, actually, a pressure release line is provided on the downstream side of the water electrolysis unit, and a pressure reducing valve and an on-off valve (solenoid valve) are disposed in the pressure release line. The pressure reducing valve is preferably inexpensive and compact. Usually, a pressure reducing valve having a free valve structure in which a pin member is pressed against a seat is used.